Sealed casing for electrolytic capacitor with pressure relief vent

ABSTRACT

A pressure relief vent for electrolytic capacitors and the like in which an impervious thin metallic disc is supported by the capacitor casing between apertured vent retainer and sealing gasket members the aperture sizes of which are selected to effect rupture of the disc at a predetermined pressure differential across the disc.

United States Patent Willy et al. 1451 Aug. 29, 1972 [54] SEALED CASINGFOR ELECTROLYTIC 2,203,902 6/ 1940 Georgiev .."..317/230 X CAPACITORWITH PRESSURE RELIEF 2,227,319 12/1940 Pontis et a1. ..3l7/230 X VENT3,280,381 10/1966 Ayer ...3l7/230 [72] Inventors: John Robert WillyEasley; Emil F. I

Blase, Pickens, both of so Primed hammer-{mes Kellen Attorney-John A.Dienner et a1. ,[73] Assignee: Sangamo Electric Company, Springfield,lll. [57] I ABSTRACT I Q [22] Filed: June 1971 A pressure relief ventfor electrolytic capacitors and [21] App1.No.: 152,820 the like in whichan impervious thin-metallic disc is p supported by the capacitor casingbetween apertured 521 US. Cl .317/230, 317/242 vent retainer and Sealinggasket membels the apeflure. 51 1111. C1. .L ..H0lg 9/12 sizes of whichare selected to effect rupmre 9f the disc. [58] Field of Search..317/230,231,233 at a p i ed p e ure differential across the disc. [56]References Cited Cl 4m Fi UNITED STATES PATEN'IS 1 2,178,686 1 1/1939Georgievet a1... ..31 7/23 0 1;

J0 I I SEALED CASING FOR ELECTROLYTIC CAPACITOR WITH PRESSURE RELIEFVENT BACKGROUND OF THE INVENTION The present invention relates generallyto electrolytic capacitors, and more particularly to a novel pressurerelease vent means therefor which is highly resistant to permeation byvolatiles in the electrolyte and malfunction of the associatedcapacitor.

'A common problem with electrolytic capacitors lies in providing areliable vent that will not leak gas or liquid at normal operatingtemperatures and pressures but which will function effectively as asafety pressure release vent when the capacitor malfunctions as theresultof improper application, dielectric failure, or being connected inreverse voltage polarity. Typical pressure release vents as heretoforeknown and used are in the most part made of elastomeric materials thatare not reliable because their operating characteristics change withheat, time, atmospheric conditions, and stresses due to pressuredifferentials. Recent developments in electrolytic capacitorshaveproduced electrolytes which have extremely adverse effects on elastomertype pressure release vents. There thus exists a need for a pressurerelease vent which is highly resistant to permeation and deteriorationby electrolyte volatiles and which will reliably release the internalpressure of an electrolytic capacitor or the like when the pressurereaches a predetermined value. The present invention meets such need andeffectively overcomes the disadvantages found in the prior art pressurerelease vents.

SUMMARY OF, THE INVENTION In accordance with a preferred embodiment ofthe present invention, a capacitor having a casing open on one end isprovided with an end plate sealingly fixed within the open end of thecasing. The end plate has an opening therethrough communicating with theinterior of the casing and supports pressure release means within theopening to release or vent internal pressure within the casing when thepressure reaches a predetermined dangerous magnitude. The pressurerelease means consists of a relatively thin metallic vent disc which issupported between an annular vent retainer member and an annular sealinggasket retained within the opening in the capacitor end plate such thatone side of the vent disc is exposed to the atmosphere surrounding thecapacitor and the other side of the vent is exposed to the interior ofthe capacitor. The vent retainer member and the gasket member haveaxially aligned apertures the sizes of which are selected to establish apressure differential across the vent disc and effect rupture thereofwhen the internal pressure within the casing reaches a predetermineddangerous value. In one embodiment, the end plate of the casing in whichthe pressure release means is mounted has a portion substantiallyoverlying the annular gasket and vent disc to prevent accidentalpuncturing of the disc during normal usage.

Accordingly, one of the primary objects of the present invention is toprovide a novel pressure release vent for electrolytic capacitors andthe like which will safely and reliably release pressure buildup withinthe capacitor casing when the pressure reaches a predeterwhich functionsas a safety pressure release vent upon mined value, while providing ahermetic seal uneffected over normal operating temperature and pressureranges.

Another object of the present invention is to provide a novel pressurerelease vent for electrolytic capacitors and the like which is resistantto permeation by volatiles contained in the electrolyte.

Yet another object of the present invention is to provide novel pressurerelease vent means for electrolytic capacitors and the like wherein thevent means consists of a thin metallic vent disc which is supported insandwich fashion between apertured vent retainer and sealing gasketmembers, the vent disc being exposed to the interior of the capacitorcasing and to the atmosphere surrounding the casing, and wherein thearea ratio of the axially aligned openings in the retainer and gasketmembers is selected to effect rupture ofthe vent disc when apredetermined pressure differential across the disc is reached. I

Further objects and advantages of the present invention, together withthe organization and manner of operation thereof, may best be understoodby reference to the following detailed description when taken inconjunction with the accompanying drawing wherein like referencenumerals designate like parts throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view ofan electrolytic capacitor employing a pressure release vent inaccordance with the present invention, a portion of the casing beingbroken away to better illustrate the invention;

FIG. 2 is an enlarged partial sectional view of the pressure releasevent mounted in the upper end cover of the capacitor casing;

FIG. 3 is a partial plan view taken generally along the line 3--3 ofFIG. 2, looking in the direction of the arrows; and

,FIG. 4'is an enlarged partial sectional view of an alternative mountingarrangement for the pressure release vent.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, andin particular to FIG. 1, the present invention will be described,'by wayof illustration, in conjunction with an electrolytic capacitor indicatedgenerally at 10. The capacitor 10 includes a hollow cylindrical casingmeans 12 which defines a substantially closed cylindrical chamber 14therein which is open at theupper end thereof prior to assembly of thecapacitor components. The casing 12 is made of a suitable chemicalelectrolyte resisting material and serves to encase a capacitor section16 of conventional design and an electrolyte which surrounds thecapacitor section 16 within the casing in a known manner. The capacitorsection 16 has electrodes l8 and 20 projecting from the upper endthereof, the electrodes being connected to suitable connector terminals22 and 24, respectively. The conductor terminals 22 and 24 are mountedin a top or upper end cover plate 26 which is sealingly secured withinthe casing 12 adjacent the upper open end thereof. The end cover plate26 will be considered as a portion of the capacitor casing means and issimilarly made of a suitable material resistant to the electrolyte, withthe connector terminals 22 and 24 being suitably electrically insulatedfrom the end plate.

The electrolytic capacitor thus far described is of generally knownconstruction. It is known in the operation of electrolytic capacitorsthat a liquid or gas pressure buildup may result interiorly of thecasing thereof when the capacitor malfunctions as the result of improperapplication, dielectric failure, or being connected in reverse voltagepolarity. The present invention is concerned primarily with theprovision of pressure sensitive release vent means for use inconjunction with an electrolytic capacitor or the like, which vent meanswill not leak gas or electrolyte fluid at normal operating temperaturesand pressures but will function as a safety pressure release'ventwhen'the capacitor malfunctions.

To the above end, I provide pressure sensitive release I vent means,indicated generally at 28, which is mounted in the top cover or endplate 26. NOTING FIG. 1, taken in conjunction with FIGS. 2 and 3, thepressure sensitive release vent means 28 is mounted within a circularrecess 30 formed in the lower surface of the end plate 26. The circularrecess 30 is of limited depth so as to establish an upper wall portion32 in the end plate which has an opening 33 therein axially aligned withthe circular recess 30. The pressure sensitive release vent means 28includes an annular vent retainer member 34 which is preferably made ofa metallic material compatable with the chosen electrolyte to be usedwithin the capacitor 10. The vent retainer member 34 has an outerdiameter which allows snug insertion into the recess 30 and includes anaxially disposed circular aperture 36 therethrough of a predeterminedsize as will be more fiilly explained hereinbelow. A relatively thinflat metallic vent disc 38 having an outer diameter substantiallyidentical to that of the vent retainer member 34 is supported directlyon the upper surface of the vent retainer member, considered in FIG. 2,so as to overlie the central aperture 36 in the vent retainer member.Preferably, the thin vent disc 38 consists of an aluminum disc ofsufficient thickness to resist permeation by the volatilescontained-within any electrolyte as might be used with the capacitor 10.

An annular sealing gasket 40 is disposed within the recess 30 betweenthe wall portion 32 of the end plate 26 and the vent disc 38, and servesto hermetically seal the vent disc within the recess 30 of the end plate26. In assembly, the annular seal 409 vent disc 38 and annular ventretainer member 34 are assembled in stacked relation and inserted withinthe recess 30 in the end plate 26, the end plate being thereafter swagedor staked over as at 42, either at intervals about the edge of therecess 30 or in a manner to provide an annular swaged retainer ridge.The vertical thicknesses of the vent retainer member 34, the vent disc38 and the annular sealing gasket 40, as well as the depth of thecircular recess 30, are selected such that the pressure sensitiverelease vent means 28 is fixedly secured and sealed within the recess 30of the end plate 26.

The annular gasket 40 has an axially disposed circular aperture 44therethrough which is axially aligned with the aperture 36 in the ventretainer member 34, the axially aligned apertures of the retainer memberand gasket being separated by the vent disc 38. In this manner, the ventdisc 38 has its lower inner surface directly exposed to the interior ofthe capacitor 10 and has its upper outer surface exposed to theatmosphere surrounding the capacitor through the circular opening 33.The relative eflective circular cross-sectional area of the aperture 44which is exposed to the vent disc 38 is selected to establish a pressuredifierential acting across the vent disc 38. The wall portion 32 of theend cover 26 adjacent opening 33 partially overlies the sealing gasket40 and a portion of the vent disc 38 to prevent accidental puncturing ofthe vent disc which, as noted, is exposed to atmosphere through theopening 33.

During operation, if the pressure within the capacitor casing 12 shouldreach a predetermined value which is determined to be unsafe, thepressure differential acting across the vent disc 36 will cause the ventdisc to rupture allowing release of the excess pressure within thecasing 12 to the atmosphere surrounding the capacitor. The specificproperties and dimensional configurations of the elements comprising thepressure sensitive release vent means 28 may vary depending upon thespecific application. In particular, the specific physicalcharacteristics of the thin metal vent disc 38 are selected such that incombination with the area of the aperture 44, the vent disc will rupturewhen interior pressure within the casing 12 of the capacitor reaches apredetermined pressure relative to the pressure of the atmospheresurrounding the casing and acting on the upper surface of the disc ventthrough the opening 33 in the upper end cover 26.

One design which has been found to be particularly useful inelectrolytic capacitors, provides an aluminum vent disc 38 which has athickness to resist permeation of the volatiles in the electrolyte andwhich is designed to rupture at a pressure differential between theinside of the casing 12 and the outer atmosphere thereof ofapproximately between and PSI. This rupture pressure may be changed byusing different vent materials, different thicknesses of the samematerial, and difierent temper or strength characteristics of the samematerial. In addition, the rupture pressure may be varied by differingthe effective diameter of the axial opening 44 within the seal gasket40. One particular embodiment of the present invention employed analuminum vent disc made of 99.99 percent pure aluminum having an 0temper and having an effective opening 44 diameter of 0.200 inches and athickness of 0.001 inch.

While one embodiment of my invention has been shown and described withreference to FIGS. l-3, it will be obvious to those skilled in the artthat changes and modifications may be made therein without departingfrom the invention in its broader aspects. For example, FIG. 4illustrates an alternative pressure release vent mounting arrangementwherein the recess 30 is formed in the upper surface of the end plate26. The annular gasket 40 is then placed in the bottom of the recess 30with vent disc 38 placed on top of the gasket 40 and the vent retainermember 34 placed on top of the vent disc 38. The vent retainer may besecured in position by swaging or by any one of several known springtype retainer methods.

We claim:

1. A closed casing having a header and an interior chamber forcontaining a material productive of variable pressures therein, pressurerelease means comprising an aperture in said header communicating withsaid interior chamber of the casing, and vent means in said aperture,said vent means being secured to said header and hermetically sealingsaid aperture and comprising a relatively thin metallic member blockingsaid aperture with at least a portion of one side thereof exposeddirectly to said interiorchamber of the casing and at least a portion ofthe opposite side exposed to the atmosphere external to said chamber insaid casing, and washer-shaped members secured to said header to sealsaid metallic member with respect'to said aperture and having theopenings thereof in registration with said aperture upon greaterpressure within said chamber causing the rupture of said sealedmetallic, member to release the pressure through said openings and saidaperture.

2. An improvement of claim 1 wherein said relatively thin metallicmember is made of aluminum material.

3. The improvement of claim 1 wherein one of said washer-shaped memberscomprises sealing gasket material for establishing the hermetic sealbetween said thin metallic member and the header.

4. The improvement of claim 1 wherein said aperture includes a circularopening in said header and wherein one of said washer-shaped memberscomprises a metal I washer and a second one of said washer-shapedmembers is of an elastomer material, and in which said thin metallicmember is located between said first and second washer-shaped members,the second one of said washer members being in direct engagement withthe upper surface of said header and having a central opening inalignment with said circular opening.

5. An improvement of claim 4 wherein said thin metallic member comprisesa thin aluminum disc and said openings of said washer-shaped members arein registration with said aperture in said header whenever said aluminumdisc ruptures in response to the interior pressure within the casingreaching a predetermined value relative to the atmospheric pressuresurrounding the casing.

6. A closed casing having a header and an interior chamber forcontaining material productive of variable pressure therein, pressurerelease means comprising an aperture in said header communicating withsaid interior chamber of the casing and vent means in said aperture,said vent means being secured to said header and hermetically sealingsaid aperture and comprising a relatively thin metallic member blockingsaid aperture with at least a portion of one side thereof exposeddirectly to said interior chamber of the casing and at least a portionof the opposite side exposed to the atmosphere external to said chamberin said casing, at

least first and second washer-shaped members, and

upon greater pressure within said chamber causing the rupture of saidsealed metallic member to release the pressure through said 0 nings andsaid aperture.

7. The combination of claim 6 wherein said metallic member consists ofan aluminum disc.

8. The combination of claim 6 wherein said metallic member comprises athin metallic disc.

9. A combination of claim 6 wherein said aperture includes a firstcircular recess of a first diameter in said header which connects withsaid interior chamber and a second circular recess of a difl'erentdiameter which connects with the atmosphere.

10.The combination of claim 9 in which the diameter of the secondcircular recess is smaller than the diameter of the first circularrecess.

11. The combination of claim 9, wherein ,said first and secondwasher-shaped members and said metallic member are snugly fit in thelarger of said first and second circular recesses and wherein saidsecuring means comprises swaging the end of said larger recess which isopposite to the smaller of said first and second circular recesses.

1. A closed casing having a header and an interior chamber forcontaining a material productive of variable pressures therein, pressurerelease means comprising an aperture in said header communicating withsaid interior chamber of the casing, and vent means in said aperture,said vent means being secured to said header and hermetically sealingsaid aperture and comprising a relatively thin metallic member blockingsaid aperture with at least a portion of one side thereof exposeddirectly to said interior chamber of the casing and at least a portionof the opposite side exposed to the atmosphere external to said chamberin said casing, and washer-shaped members secured to said header to sealsaid metallic member with respect to said aperture and having theopenings thereof in registration with said aperture upon greaterpressure within said chamber causing the rupture of said sealed metallicmember to release the pressure through said openings and said aperture.2. An improvement of claim 1 wherein said relatively thin metallicmember is made of aluminum material.
 3. The improvement of claim 1wherein one of said washer-shaped members comprises sealing gasketmaterial for establishing the hermetic seal between said thin metallicmember and the header.
 4. The improvement of claim 1 wherein saidaperture includes a circular opening in said header and wherein one ofsaid washer-shaped members comprises a metal washer and a second one ofsaid washer-shaped members is of an elastomer material, and in whichsaid thin metallic member is located between said first and secondwasher-shaped members, the second one of said washer members being indirect engagement with the upper surface of said header and having acentral opening in alignment with said circular opening.
 5. Animprovement of claim 4 wherein said thin metallic member comprises athin aluminum disc and said openings of said washer-shaped members arein registration with said aperture in said header whenever said aluminumdisc ruptures in response to the interior pressuRe within the casingreaching a predetermined value relative to the atmospheric pressuresurrounding the casing.
 6. A closed casing having a header and aninterior chamber for containing material productive of variable pressuretherein, pressure release means comprising an aperture in said headercommunicating with said interior chamber of the casing and vent means insaid aperture, said vent means being secured to said header andhermetically sealing said aperture and comprising a relatively thinmetallic member blocking said aperture with at least a portion of oneside thereof exposed directly to said interior chamber of the casing andat least a portion of the opposite side exposed to the atmosphereexternal to said chamber in said casing, at least first and secondwasher-shaped members, and means for securing said washer-shaped memberswithin said aperture with said metallic member disposed between thewasher-shaped members, one of said washer-shaped members being of anelastomer material providing gas and liquid-tight seal between saidwasher members and said header, said washer-shaped members havingopenings in registration with said aperture upon greater pressure withinsaid chamber causing the rupture of said sealed metallic member torelease the pressure through said openings and said aperture.
 7. Thecombination of claim 6 wherein said metallic member consists of analuminum disc.
 8. The combination of claim 6 wherein said metallicmember comprises a thin metallic disc.
 9. A combination of claim 6wherein said aperture includes a first circular recess of a firstdiameter in said header which connects with said interior chamber and asecond circular recess of a different diameter which connects with theatmosphere.
 10. The combination of claim 9 in which the diameter of thesecond circular recess is smaller than the diameter of the firstcircular recess.
 11. The combination of claim 9, wherein said first andsecond washer-shaped members and said metallic member are snugly fit inthe larger of said first and second circular recesses and wherein saidsecuring means comprises swaging the end of said larger recess which isopposite to the smaller of said first and second circular recesses.